1. Field of the Invention
The present invention generally relates to a motorcycle. More particularly, the invention relates to a frameless motorcycle constituted such that a swing arm adapted to support a front wheel at the front end thereof is pivotably attached at its rear end to the front part of a power unit disposed in the middle of the vehicle, without employing a so-called vehicle body frame.
2. Description of Relevant Art
Conventionally, most general motorcycles have been of a type employing a so-called vehicle body frame.
In this respect, in recent years, there have been proposed motorcycles of a type constituted, without employing a vehicle body frame, such that a swing arm supporting a front wheel at the front end thereof is pivotably attached at its rear end to the front part of a power unit disposed in the middle of the vehicle. Thus, in this type of motorcycle a front fork, as conventionally used, is omitted. As an example thereof, there is one that is disclosed in U.S. Pat. No. 4,265,329.
In the frameless motorcycle according to the United States Patent above, a plate member is fixed to the front end of an engine of a power unit arranged in the longitudinal direction of the vehicle, and a pair of swing arms, arranged one above the other and adapted to steerably support a front wheel at the front ends thereof, are vertically swingably pivoted at the respective rear ends thereof on the plate member.
Moreover, in the United States Patent above, it is suggested that the engine itself may have a projected portion to substitute for the plate member.
Further, with respect to the motorcycle according to the United States Patent above, it is said that, because of the omission of what is called a vehicle body frame, the vehicle weight is reduced in comparison with motorcycles of the type employing a vehicle body frame.
In the motorcycle according to the United States Patent above, however, since the swing arms are pivotably attached substantially to the engine itself, the strength and rigidity of the engine itself are required to be correspondingly secured, thus raising such a problem that the engine as well as the entirety of vehicle may be restricted in freedom of design.
With such points in mind, the present invention has been achieved to effectively solve a problem in conventional frameless motorcycles.